Inverters/rectifiers and DC/DC converters critical for supporting high-power, high-voltage systems, such as hybrid-electric ground vehicle propulsion systems, typically operate between two high voltage busses with bi-directional power flow of up to hundreds of kilowatts. To prevent system damage during fault conditions, bi-directional fault isolation, or power conditioning, is needed. Because mechanical contactors do not provide adequate actuation times and suffer severe degradation during repeated fault isolation, a solid-state circuit breaker (SSCB) is desirable.
To provide such a SSCB, and to enable such bi-directional power flow in a semiconductor device, the device should provide symmetric current flow in forward and reverse directions and blocking of a specified voltage in forward and reverse directions. In addition, the gate-drive of the bi-directional circuit should operate at high current-gain and high bandwidth with low conduction losses, should allow for fast switching, and should have small physical size, all of which contribute to the bi-directional circuit's efficiency.
For the circuit of FIG. 6 in no fault efficient circuit-breaker operation, current flows with all the vertical-channel junction gate field-effect transistor (JFET) pn-junctions turned off based on Eqs. (3) and (4) (see below). In a fault event, abrupt rise in drain current and voltage will occur. The gate-source JFET junctions are always off by default gate-drive biasing. For the JFET conducting in the drain-source direction, no bipolar current due to “fault condition” is generated as the increase in drain current/voltage biases the gate-drain pn-junction more negatively. For the JFET conducting in the source-drain (reverse) direction, however, bipolar current due to “fault condition” is generated as the increase in drain current/voltage biases the gate-drain pn-junction more positively. Once the built-in potential of the gate-drain junction is exceeded (Eq. (3) and (4) are no longer satisfied), bipolar gate current starts to flow and a rise in the gate-drive current is observed.
In addition to abrupt rise in current/voltage, a fault condition will also lead to higher JFET temperatures. JFETs have positive temperature coefficients and therefore the gate-drain pn-junction built-in potential is reduced with temperature; bipolar current will flow at lower voltages. For example, a SiC pn-junction with doping levels relevant to power applications turns on at ˜2.7 V at room temperature. At 150° C., the junction will turn on at ˜2.4 V. Typically, in no-fault conduction of 1000 A, the gate drive current is below 1 nA. Should a fault occur, the turned on gate-drain junction will conduct Amps if the circuit does not abruptly go into blocking mode.
Thus, a need exists to provide a system and method to detect a fault condition and bias the JFETs so that they operate as a solid state circuit breaker.
Therefore, it is desirable to provide a system and method for providing an optically triggered circuit breaker.
Advantages of the present invention will become more fully apparent from the detailed description of the invention hereinbelow.